I'm considering repurposing a part of a rice farm into a farm house. I've seen this done elsewhere and after about 10 years, the entire floor just sank. (I saw in 10 years, didn't know the situation before). My question is what special considerations should I keep in mind to ensure that ground is solid. I will make a brick and mortar house.
Two things cause soil subsidence in this context. 1) is the oxidative and also anoxic decay of all the accumulated organic matter that settles into the bottom of the rice pond through the decades, and 2) is soil deformation and slow flow due to the water content of the subsoil (which water leaks laterally out of the remaining ponds nearby).
You can't do anything about settling due to decomposition of organics in the soil; note that this process also releases significant amounts of methane and carbon monoxide under the structure, which can then diffuse upwards and accumulate in the crawlspace to hazardous concentration levels.
Avoiding soil deformation and flow requires that the structure be positioned far enough away from the ponds that the subsoil remains dry.